# How uncertain is a ceramic unit's process carbon dioxide figure under the Intergovernmental Panel on Climate Change guide, and what drives it?

Canonical: https://senseible.earth/answers/ipcc-ceramic-process-co2-uncertainty-weighing-assay-purity

Small if you measure, large if you assume. The Intergovernmental Panel on Climate Change (IPCC) puts weighing carbonates at 1 to 3 percent uncertainty, their chemical analysis at 1 to 3 percent, and a purity assumption at plus or minus 1 to 5 percent. A European reference quoted by the guide puts clay carbonate at 0 to over 30 percent.

## The guide's numbers

- Emission factor: negligible uncertainty, if the activity data are collected correctly and the right factor is used, because it is a fixed chemical ratio.
- Weighing or proportioning the carbonates for an industry: 1 to 3 percent, if the carbonate is allocated to the right industry.
- Chemical analysis of carbonate content and identity: 1 to 3 percent.
- Assuming a purity where only carbonate rock data exist: plus or minus 1 to 5 percent.
- Using the Tier 1 or 2 default of 85 percent limestone and 15 percent dolomite: the guide says it varies with country circumstances, and gives no number.

## Where the big uncertainty sits

The note to the 10 percent clay carbonate default says a European reference reports clay carbonate contents from 0 to over 30 percent. Against 1 to 3 percent for weighing, a guessed clay carbonate share swamps everything else. So the first record to improve is an assay of your own clay, not a finer weighbridge. That ordering is my reading.

## Adding the errors

The guide does not combine these for a single unit. As a worst case, if weighing and analysis both sit 3 percent high, the carbonate tonnes are off by about 6 percent. That sum is mine; the guide's Volume 1 has its own way of combining uncertainties, which I did not check.

## The unspecified line

The guide warns that national statistics with an other unspecified uses line raise uncertainty. The same warning fits a purchase ledger line such as limestone, miscellaneous. Keep carbonate bought for the kiln apart from carbonate bought for anything else. This is my reading.

## Ten tonnes of limestone, three ways to be wrong

- Base: 10.0 x 0.43971 = 4.397 tonnes of carbon dioxide (CO2)
- Weighing 3% high: 4.397 x 1.03 = 4.529 tonnes
- Weighing and analysis both 3% high: 4.397 x 1.03 x 1.03 = 4.665 tonnes, 6.1% above base
- Purity assumed at 95% when the rock is 92%: 9.5 against 9.2 tonnes of carbonate, 3.3% too high

Quantities and the 92% purity are example numbers.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the fuel and power lines of a furnace or kiln are on file. In the self-serve product it does not run clay assays or weigh carbonates; those records and their error bands are yours.

- [Process CO2 for clay products without an assay](https://senseible.earth/answers/process-co2-from-clay-bricks-tiles-without-lab-assay)
- [Default against carbonate-by-carbonate check](https://senseible.earth/answers/ipcc-ceramic-default-versus-carbonate-by-carbonate-check)
- [Is my lab CO2 factor within the IPCC range](https://senseible.earth/answers/is-my-lab-co2-factor-within-ipcc-default-range)
- [Fuel activity data uncertainty](https://senseible.earth/answers/ipcc-industrial-fuel-activity-data-uncertainty)

Sources: [IPCC, 2006 Guidelines, Volume 3, Chapter 2: Mineral Industry Emissions](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/3_Volume3/V3_2_Ch2_Mineral_Industry.pdf)

Last reviewed 2026-11-06. Quotes and figures are from the 2006 IPCC Guidelines, Volume 3, Chapter 2. The 2019 Refinement was not checked for this page; check it if a buyer names it.